MAYBE LOW-FAT FOODS MADE US EAT MORE
The theory: The low-fat food fad made us fatter. We ate high-carb foods that weren't as satisfying -- and, by gosh, we ate more as a result.
The research: In 1990, federal health officials recommended for the first time that Americans should eat less fat to lower their risk of heart disease. Many people believe that they've gained weight on such diets. Low-fat diets are generally high-carb diets. And, Dr. David Ludwig of Harvard Medical School would say that too often they have a high glycemic load.
When people diet successfully, their metabolism slows down. That slows down any continued weight loss they might hope to have. But research with mice and people has shown that how much your metabolism slows down depends on what you eat.
In one study, Ludwig and his colleagues found that metabolism slowed down about twice as much for those on a low-fat diet compared with those on a diet with a low-glycemic load (meaning foods that are digested and absorbed slowly, producing only gradual rises -- not rushes -- in blood sugar and insulin).
Those on the low-glycemic load diet also felt less hungry, perhaps because of fewer blood sugar crashes.
Our experts weigh in: Everybody has a body weight "set point," Ludwig says. "If your weight falls below that point, the body has compensation mechanisms to try to kick it back up." A diet with a low-glycemic load lowers the set point, he adds, "so you don't run into a brick wall so soon."
Susan Roberts of Tufts University thinks low-glycemic diets are a legitimate option for losing weight, but she doubts that high-glycemic load diets are a cause of the obesity epidemic. "Just think about the 1950s," she says. "Everyone was eating white bread, meatloaf (made with white breadcrumbs), potatoes and rice -- and were much thinner than today."
Barry Popkin of the University of North Carolina says there's plenty of evidence that a variety of dietary patterns will sustain weight loss -- low-fat and high in complex carbs; low-carb and high in lean proteins; diets higher in fat. "The issue is cutting calories," he says. "All do work for the short term and few work for the long term without strong self-control, family support, and exercise."
